Three Resistance States Achieved by Nanocrystalline Decomposition in Ge‐Ga‐Sb Compound for Multilevel Phase Change Memory

Abstract

AbstractPhase‐change memory (PCM), using the fast and reversible transition between crystal and glass to store binary data, is a promising candidate for next‐generation information storage and computing technologies. Recording more than one bit of information on each memory cell, known as multilevel cell (MLC) technology, can greatly increase the data density of PCMs. In this paper, the MLC capability in a phase change material Ge‐Ga‐Sb (GGS) is explored. Using the “SET” operation with increasing voltage amplitudes on this PCM cell in a 250 nm pillar structure device, three resistance levels are achieved and can be stabilized within large operating voltage windows, allowing large tolerance of SET voltage variation which may lead to the overlap of the neighboring resistance levels. It is discovered that the additional resistance level other than “0” and “1” is enabled by compositional phase separation in the nanocrystalline GGS, as revealed via atom probe tomography and electronic microscopy. The device also shows small resistance drift (ν = 0.025) in amorphous state, about four times lower than prototypical Ge‐Sb‐Te‐based PCMs, stabilizing it against time variation. Meanwhile, high thermal stability (Tc ≈ 300 °C) in GGS‐based device can also facilitate the practical applications in some extreme conditions.